An optical integrator (hereinafter simply referred to as an “integrator”) is known as an optical system that is used to uniformly illuminate an area. An integrator includes two lens arrays disposed in parallel, each of the lens arrays having a plurality of lenses (small lenses) densely arranged therein, which is known in the art as a fly's-eye lens. A non-uniform light flux incident on one of the lens arrays is divided into a plurality of segmental light fluxes, which are then superimposed and focused on the illuminated area.
It is known to employ an integrator-based illumination system in a projector, which is one type of projection-type display apparatus. On the other hand, there have been proposed projectors of this type including a plurality of illuminants in order to meet a need to increase the brightness of projected images (see, e.g., Japanese Patent Publication No. 2000-3612).
In the integrator described above, the images of the plurality of illuminants are formed on the light exiting-side second lens array. However, since the images of the plurality of illuminants are not on the optical axes of the small lenses arranged in the second lens array, the images produced when the segmental light fluxes exited from the integrator are superimposed and focused on the illuminated area may be blurred.